1. Field of the Invention
This invention relates to a prosthetic bearing element and to an implant incorporating such an element.
2. Description of the Prior Art
Prosthetic bearing elements are employed in many prosthetic implants and can be made from various materials, for example, polyethylene or nylon, provided the bearing material is compatible with the human body.
Such elements are usually held in a metal housing which carries the load although, in certain circumstances, they may be used by themselves, for example as an acetabular cup. Typical use of such elements is in knee prostheses where they are used on a tibial tray and cooperate with a femoral component. They are also used in patella constructions and act between the femoral and patella components. Yet another use, as referred to above, is as bearing cups in hip implants.
A favored material, at the present time, is polyethylene, particularly ultra high molecular weight polyethylene (UHMWPE) with a molecular weight greater than 1,000,000. It has been found however, that even this material wears and the present Applicants have therefore carried out research into the possibility of treating the material to improve the wear qualities. It has been found that a multi-axially molecular orientation in the material provides such qualities.